Archery bows have a long history of use for both hunting and sport. Some bows, including compound bows and crossbows, include cams that are mounted at the opposite ends of the bow. The cams are usually mounted in a symmetric fashion, and may include two stacked pulley or engagement sections, each with grooves, for receiving bowstrings or power cables. In operation, the cams work in conjunction with the bowstring and the power cable in the following manner. When the bow is cocked, the bowstring unwinds from the cams as they rotate. Simultaneous with the drawing of the bowstring during cocking of the bow, segments of the power cable are taken up by the cams as they rotate. The power cable thereby exerts tension on the limbs which then bend inward, storing energy. When the bow is fired, the cams rotate and release the tension on both the bowstring and power cable (and the limb) to propel the arrow forward.
One issue with conventional crossbow designs is that the cams are exposed to potential damage during transport, storage and use of the crossbow. This is because the cams are mounted on the outside profile of the crossbow. Consequently, part (e.g., one-half or more) of the cams protrude beyond the outer surfaces of the limbs. For example, a cam with its axle mounted directly to the limb necessarily extends outward beyond the limb. This is because the radius of the cam is typically larger than the size of the limb end so that the cam can take up and release a sufficient amount of the power cable. When the crossbow is placed on the ground or floor, or in a box or container, or is unintentionally bumped into a tree, person or other object during transport, the axles of the cams may be bent or loosened, the internal bearings of the cams may be deformed or misaligned, the cam grooves may be damaged, or the bowstring or power cable may be damaged.
In addition, the conventional crossbow designs have a relatively wide profile. This is caused, in part, by the protrusion of the cams beyond the outer surfaces of the limbs. This wide profile can make it difficult to use, store and transport crossbows.
Another drawback with conventional archery bow designs is that, upon firing of the bow, the limbs can undergo considerable oscillation. Such oscillations may lead to inaccurate shooting and potential torsional stress on the limbs, the cams, the bearings, and other mechanical components. The oscillation can be due to the torque on the limbs during the firing process, because of the large amount of force that is released upon rotation of the cams.
A further problem with conventional crossbow designs is that cam placement can limit the power stroke of the crossbow. For example, the distance between the trigger and the cams can determine the power of the stroke upon shooting of the crossbow. The crossbow cams are typically mounted at the limb ends, which are typically positioned at the rear ends of the limb, closer to the trigger.
Attempts have been made to increase the crossbow power stroke through the use of an inverted limb technology. In an inverted limb technology, the concavity of the limb faces towards the target. However, the inverted limb approach is generally more difficult to use, requires modifications to traditional archery techniques, and does not improve vibration tolerance of the crossbow. Further, the inverted limb approach increases the overall profile size of the crossbow because less of the barrel is within the profile, leading potentially to sensitive components being vulnerable to damage when the crossbow is placed on the ground.
An additional disadvantage with conventional crossbow designs relates to the placement of the bowstrings and the power cords. Specifically, because the barrel of the crossbow resides in the space between the bowstrings and the power cord, sufficient spacing is required for the arrow and its fletching to pass through the space without interference. With the conventional crossbow designs, the power cord is routed, at a downward angle, through a slot in the barrel.
This angle, which is relatively large, can cause several problems related to the crossbow. First, the power cable force, applied at this relatively large angle, causes or urges the cams to lean or tilt. This tilting can cause asymmetric rotation and bearing function of the cams and can also increase the wear and tear on the bearings. This tilting can also cause the limbs to twist relative to each other or otherwise assume a distorted shape. In addition, the application of the power cable force along this relatively large angle can lead to inefficiency and loss of force transmission from the power cable to the limbs during the firing of the crossbow. All of these problems can result in both a decrease in shooting performance and increased wear and tear on components, and can require more frequent replacement of power cables and other components of the crossbow.
The foregoing background describes some, but not necessarily all, of the problems, disadvantages and shortcomings related to conventional archery bow technology.